The present invention relates to a manganese based catalyst for use in a metal-air electrochemical cell, and more particularly, relates to the composition and manufacture of an air electrode comprising said catalyst.
Metal-air electrochemical cells utilize oxygen from the ambient air as a reactant in an electrochemical reaction to provide a relatively lightweight power supply. Generally described, a metal-air cell includes an air-permeable cathode and a metallic anode separated by an aqueous electrolyte. During the operation of a metal-air cell, oxygen from the ambient air is reduced at the cathode to form hydroxide ions. The metal is oxidized at the anode and reacts with the hydroxide ions, such that electrons are released to provide electrical energy.
Most air electrodes are either inherently or by purposive implementation, catalytically active. Although effective air electrodes are available, there remains a need for air electrodes with enhanced catalytic activity. An important factor in optimizing electrode performance is catalyst particle dispersion. The more uniformly the catalyst is dispersed and the smaller the size of the catalyst particles, the higher the activity of the air electrode. With conventional methods of catalyst production it is difficult to reduce the particle size of the catalyst enough to uniformly distribute it throughout the active layer of the electrode. The method of the present invention produces an oxygen reduction catalyst wherein the catalyst particles are small enough to be uniformly distributed within the electrode.
The present invention fulfills the above-described need by providing a method of producing a manganese based oxygen reduction catalyst for use in an air electrode using a sol-gel process. This invention also encompasses the resulting catalyst, a cathode comprising said catalyst and methods of making a cathode comprising said catalyst. Surprisingly, the sol-gel method produces a catalyst having particles sizes which are submicron and easily dispersed throughout a catalyst support.
More particularly, the present invention relates to a method of producing a manganese based oxygen reduction catalyst wherein a solution of a manganese alkoxide and an alcohol is prepared. Water is added to the solution to form a sol and then the sol is heated to a temperature sufficient to remove the alcohol and form a gel. The gel is mixed with activated carbon and heated at a temperature between 150xc2x0 C. to 250xc2x0 C. to form a manganese oxide.
The present invention also relates to an air cathode comprising the above-described catalyst. More particularly, the air cathode comprises an active layer including the oxygen reduction catalyst of the present invention. In addition, the air cathode includes a current collector in electrical contact with the electrode. The active layer of the air cathode further comprises carbon black and a non-wetting agent/binder such as polytetrafluoroethylene.
More particularly, the active layer is formed by admixing the manganese based catalyst with an adsorptive particulate material, such as carbon black, and a non-wetting agent/binder, such as polytetrafluoroethylene.
Other objects, features, and advantages of this invention will become apparent to those skilled in the art upon understanding the foregoing detailed description and accompanying drawings.